This invention relates to apparatus and method for cutoff register control for diaper machines and, more particularly, to apparatus and method employing strobe light imaging prior to diaper cutoff.
Disposable diapers generally consist of an absorbent pad confined between a moisture impervious web (polyethylene) and a moisture pervious (non-woven)--see co-owned U.S. Pat. Nos. 4,417,935; 4,543,141; 4,701,239; and 4,711,683. These are made continuously by advancing one of the webs along a longitudinally extending path, applying the absorbent pad material and then applying the second web. The webs are usually longitudinally folded to provide a more compact product after which the webs are transversely severed between pads to provide diaper lengths of predetermined size.
There has been a problem in the precise location of the cutoff. Cutoff registration systems have long been in use. For example a scanner would sense the pad leading edge and a signal would be issued to advance or retard the position of the cutoff roll. However, this operation was not exact and it was felt that a video imaging system would make it possible to obtain a much improved measurement of the pad edge. One of the problems however, is that the "video snapshot" must be accurately timed to properly "frame" the diaper--in contrast to the previously employed registration scanner which looked continuously for the pad edge.
The typical method for registration using a video imaging system is to employ a scanner or other trigger device to time the picture and then analyze the image to measure the distance between features on the object. This has presented another problem in the case of diaper cutoff because there is no convenient view of the final diaper, the same having been folded before cutoff. Additionally, the elastic in the diaper causes the contract and change shape after cutoff so that image analysis is very difficult.
This invention describes a means and method for achieving the improved video sensing using a simple, practical means and method. More particularly, the invention controls the cutoff by strobe light imaging the leading pad edge and a point fixed in space prior to cutoff, comparing the imaged distance between the pad edge and the fixed point with a predetermined value range and thereafter adjusting the means for cutting and concurrently the strobe trigger point to bring the distance into the value range.
Now that the diaper picture is staying in the proper reference frame because the strobe timing adjusts to keep it there, the other registration measurement points for the diaper can be taken and all portions of the diaper can be registered to exact dimensions.
Now that the image of the diaper is always within the frame of the camera, registration of the fluff cutout, final cutout, foam placement, tab placement is achieved by using line measurements from the fixed reference point to each register point in the diaper. Each registration point is then motor controlled to bring the points into specified limits.
Other objects and advantages of the invention may be seen in the details of construction and operation set forth in the ensuing specification.